Bought two of these, one for my office, one for my younger child's bedroom.
My plan? Simple - schedule the one in my office as the primary sensor while the kids are in school (work from home), and schedule the one in my daughter's bedroom to be the primary during the night (keep her comfortable), and then for pre/post school and on the weekends when they're awake, use the downstairs main thermostat as the primary.
Here's what actually happened. Bought two of these sensors unpacked, scanned the QR code (note: if you buy more than one and take the tabs out and get confused as to which QR code goes to which sensor, take a coin and unscrew the back, there is a QR code on the inside as well. Had to apply more strength/pressure on unscrewing the back ring than I had anticipated...), added the new sensor to my Nest account/system.
Tried to connect to the thermostat downstairs, kept saying it couldn't establish a connection, move the sensor closer. Kept moving it closer and closer until I literally rested the sensor on top of the actual thermostat and it still said it couldn't make a connection. That's when I unscrewed the back of the sensor trying to make sure the battery was seated properly, etc. It was. Tried again, failed.
Removed the sensor from the nest account, tried to re-add and re-sync, no luck. Then I realized that (for the first time in probably ever...) the main thermostat was not connected to my WIFI network, and hadn't been for about 2 hours. Seems like something the setup of this remote sensor should check for... like maybe a "hey, seems like your thermostat has lost its connection to your home network, and that's required for setup of this newly added device".
I rebooted the main thermostat and the connections worked flawlessly, even through a few walls.
If you have the nest cameras (I have one in each kid's room), and you use the default labels "office, den, kids room, bedroom, whatever" and the labels match, it will show you the temperature in the room where the camera is, which is kind of a cool feature.
Anyway, then when it came time to schedule the priority of all the sensors I was a little disappointed with how "locked-in" the scheduling is. You have the options to set priority of sensors by "night, morning, mid-day, and evening". The time periods are all locked and not adjustable. You also can not set priority by the day of the week, it's just one generic priority schedule for every day of the week with locked time periods.
Seems like it wouldn't be too difficult to allow this functionality (And for that matter custom label names for sensor/camera/thermostat locations).
Final thing to note is the sensor is a lot smaller than I was expecting. About the size of a flattened ping-pong ball, and very light. You also have the option of just putting it on a shelf rather than drilling a hole in the wall and mounting it. Should allow you to experiment with locations or change rooms easily if it's not working exactly the way you want it to.
Overall, though, great product, does what it should. Took 1 star off because of the lackluster scheduling that could be improved, and because the setup process did not make a basic check to see if the thermostat was still connected to WIFI and let me waste about 30 mins trying to set it up before I found out myself.